Thread strength and friction tester



1956 E. B. FREDERICK ETAL 2,730,891

THREAD STRENGTH AND FRICTION TESTER 2 SheetsSheet 1 Filed Oct. 29, 1954 INVENTORS Eciwcud Bfiederzlcif Fi'edQIic/(Ffialas ATTORNEY Jan. 17, 1956 E. B. FREDERICK EI'AL 2,730,891

THREAD STRENGTH AND FRICTION TESTER 2 Sheets-Sheet 2 Filed Oct. 29, 1954 INVENTORS ATTORNEY United States THREAD STRENGTH AND FRICTION TESTER Edward B. Frederick, Needham, Mass, and Frederick F. Balas, Pennsauken, N. J., assignors to the United States [of America as represented by the Secretary of the rmy Application October 29, 195d, Serial No. 4657M 6 Claims. (Cl. 73-12) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to apparatus for testing the strength of sewing thread by means of impact energy and for imposing frictional resistance on the thread under test.

The sewing eiliciency of threads, i. e., their sew-ability under production conditions without excessive breakage, has long been a concern of the garment industry. New high speed sewing machinery, modern methods of finishing fabrics, and the use of new synthetic fibers in cloth have all served to increase the seriousness of the problem. Threads with low sewing efiiciency result in much loss of production time, cause frequent seam repairs to be made, and produce many imperfect garments. Maintenance of sewing machines has also been complicated by repeated thread failures, and in Governmentoperated factories the problem has become a threat to efiicient and economical production.

Some of the leading sewing thread manufacturers use a machine-loading apparatus to test their thread. Basically this apparatus is a modified lock-stitch sewing machine with an attachment permitting the thread to be sewed under gradually increased tension, applied by means of a dead weight loading device, until breakage occurs. This machine, if very carefully adjusted and used by the same well trained operator, will give fairly reproducible results; however, its adjustment is so critical for eilicient operation that it cannot be considered satisfactory for the acceptance-testing of Government-purchased thread.

After study of the problem, we have concluded that the cause of unsatisfactory sew-ability of thread is either insufiicient impact strength or poor frictional characteristics or both of these deficiencies.

The present invention aims to provide a simple, easily handled apparatus which subjects a sample of the thread under test to an impact sutlicient to break it, which measures the amount of energy necessary to break the thread, and which imposes an adjustable frictional resistance on the thread while thethread moves a predetermined distance before breaking. The friction device insures that (a) the thread under test has not been touched, (12) test specimens are randomly selected throughout a thread cone, and (c) the thread has been mechanically conditioned by being pulled at a fairly uniform tension.

Other objects and advantages of the invention will be apparent from the following description of a preferred embodiment of the, invention shown in the accompanying drawings, in which:

Fig. 1 is a perspective View of the device;

Fig. 2 is a top plan view of the same, with parts in section;

Fig. 3 is a diagrammatic view of the device;

Fig. 4 is a sectional elevation on a full size scale showatent I ing the pendulum shaft, and its bearings, the scale plate, the impact arm, the pointer and other elements;

Pi 5 is an elevation showing the thread-guiding pins, the friction guide, the slotted member, and other elements;

Fig. 6 is a detail in section showing a thread clamp;

Fig. 7 is an exploded view of the thread clamp of Fig 6;

Fig. 8 is an exploded view of the latch and its support.

Referring particularly to the drawings, we have shown a portable testing machine or device adapted to be placed on a table or like support and comprising a pedestal it an upright H which is shown as an inverted U-shaped standard integral with the pedestal, a semicircular scale plate 112 fixed by screws to standard lit to lie in a vertical plane, a horizontal arm 14 fixed to the upper end of standard ii, a pendulum l5 pivotally supported to swing between the two legs of upright ii, a latch lever 16 swingably supported at its upper end on horizontal arm l t, a keeper 17 on the pendulum engageable with latch lever lo, a thread clamp 55 fixed to the free end of pendulum 15', and an indicator arm or pointer 19 movable over the face of the scale plate lndicia 2s forming a scale divided into arbitrary units are marked on the scale plate adjacent its outer or arcuate edge, and the outer pointed end of indicator arm l9 moves over said scale when a test is being made as will be described.

T e inner or pivoted end of pendulum 15 is fixed to a horizontal shaft M which is supported in ball bearings 22, 23 that are mounted in the legs of standard ll, see Fig. 4-. An impact arm is rigidly fixed to one end of shaft Ill so as to lie in the same general plane as the pendulum and swing with it. When the pendulum is released from its horizontal, latched position by depressing button lo thus swinging latch lever to away from keeper i7, impact arm 24 will descend with the pendulum; but while the pendulum swings freely and contacts nothing, impact arm will strilre a lug fixed to and projecting outwardly from the indicator arm The indicator arm is not fixed to any part, hence it will swing upwardly (clockwise) in response to the blow struck by impact arm Obviously, the extent of upward swing of the indicator arm depends on the energy of said impact, and the scale Qlti will measure the highest point of said upward to give a reading which may be noted by the operator in his record of the ten initially the indicator arm is vertical and touches a stop or abutment 2E5 tired to the scale plate to insure that the indicator arm in its initial posmou reads sero on the scale. As shown in 4, the indicator arm has an adjustable frictional mounting to hold "the arm in an position above the zero position into which it may he moved by the impact arm. The frictional mounting includes washers 2Y3", on opposite sides of the inner end of the indicator arm, a thin nut threaded on a screw threaded nipple 3d which surrounds shaft 2i, said nipple being fixed to the scale plate by means of aged head 31 located 4 threaded on nipple Sit on the opposite side of the Lidl'lflifll arm from nut 29, and a loci: ut threaded on nipple: ii and adapted to be set up against the bossed nut 32 alter the latter has been properly adjusted. i'vl'lcn nuts m and 33 are loosened, the indicator arm will swing f ly or loosely about the axis of shaft ill, but when said nuts are carcfully tightened, the indicator arm will swing, when kno led by the impact arm, and will remain in the highest position reached in said swing. The friction adjustment should be such as will prevent an overshoot of the indicator arm clue to its kinetic energy.

A weight 36 is slidable on the pendulum and is secured in adjusted positions by set screw 37, so that the impact and hence the extent of swing of the indicator arm may be varied. When testing strong or coarse thread, weight 7 3 36 will be adjusted out toward the free end of the pendulum; Latch. lever 16 and keeper 17 may also be adjusted longitudinally of the pendulum. If preferred,

units of length may be marked as a scale on the penduthe operator working with the testing device. A predetermined length of thread is drawn off from cone 42 and cut and one end of the thread length or specimen 43 is made fast to clamp 55 on the end of the pendulum. The specimen is then trained around three guide pins 45. 46, 47 fixed to a vertical arm 43 that is clamped on bar 40. A pair of guide pins may be used, if preferred. The specimen passes from the pins through a friction guide 49 which comprises two fiat friction disks between which the thread travels, and a weight 50 which presses the upper'friction disk against the lower. Weight 50 should be about 20 oz. for best results. From the friction disks the specimen may extend through a wedge-shaped slotted member 51 (Fig. 3) and one inch beyond said slotted member the thread is knotted as shown at 52, the slot being so narrow that the knot can not pass through it. When the pendulum is released the specimen will slide one inch through the friction guide 49 before knot 52 catches in the slotted member 51 and stops movement of the thread. The specimen will then break. In lieu of knot 52, a small stop (not shown) may be clamped to the specimen at the proper point to make sure that the specimen slides one inch only through the friction guide and then breaks. A spring-clamp could be used as the small stop mentioned above.

In lieu of the slotted member 51, a clamp 55 may be provided which may be adjusted to offer a narrow passage or slot for free movement of the thread specimen but preventing knotp52, or the thread stop previously mentioned, from moving through it. In Figs. 1 and 2, the same kind of clamp 55 is shown both on the end of the rod pendulum, to clamp the specimen firmly, and on bar 40, to permit the one inch thread movement referred to above. Referring to Figs. 6 and 7, clamp 55 consists of an 'L-shaped jaw member 56, a cooperating flat jaw member 57, a pair of parallel studs 58 screwed tight into one arm of jaw member 56 and fitting in'bores 59 extending transversely through jaw member 57, and coil springs 60 received in counterbores 61 in flat jaw 57. A cam lever 62 having a cam 63 on one end is pivoted on a bolt 64 whose end passes through a bore 65 in an arm of jaw member 56, with a nut 66 to secure the bolt. Cam 63 works against a fiat outer face 67 on jaw member 57, which is a cam follower. Coil springs 60 tend to hold the jaw 57 away from the L-shaped jaw 56, so that the operator may adjust cam lever 62 to provide the desired space or slot for thread movement.

Referring to Figs. and 7, vertical arm 48 supports friction guide 49 by means of a horizontal arm 70. A rod 71 is secured at one end to arm 70 to extend upwardly at an acute angle, and the other end of rod 71 is reduced as shown at 72 to provide a support for clamp 55. L- shaped jaw 56 has a bore 73 which closely fits the reduced rodend 72 to hold the clamp on the rod end by friction. Fig. 5 shows how disc spacers or washers 74 may be used to adjust the elevation of the fiat friction disks or friction guide 49. Bore 73 has screw threads 75 for 'at least part of its length, which permits use of a screw 76 (Fig. 6), passing through pendulum 15, to secure clamp 55 on the pendulum near its free end; The thread specimen is securely clamped to the pendulum end by moving cam lever 62 as far around as possible.

Cit

, 4 The energy used to move the indicator arm against the friction of its mounting causes an error in the reading, hence this friction must not be any larger than'necessary.

The total energy absorbed from the pendulum is the quantity recorded in a test, and this isequal to the energy necessary to rupture a specimen, which is the quantity to be measured, plus the frictional and kinetic energy ab sorbed by the indicator. The above-mentioned error in the reading can be corrected by a simple procedure described in National Bureau of Standards Report No. 3138 dated February 25, 1954; OQMG'Project No. 92-06-05. As explained in said report, the correct value of the energy to break a specimen in an impact test, that is, the energy absorbed from the pendulum is given by the following expression:

Reference should be made to the diagram, Fig. 3. In the above expression, It is the test reading, I0 is the maximum swing position of the indicator arm after the pendulum has swung several times free of the thread, It is'the swing position of the indicator arm after the first release of the pendulum, also free of the thread, Q is the angle between the vertical and the final position of the indicator arm, and hi) is the angle between the vertical and In.

There are two ways of using the described apparatus. One end of the specimen may be clamped to the pendulum and the specimen may then be passed around the guide pins 45, 46, 47, through friction guide 49, and finally secured to fixed clamp 55. The second manner of use is shownin Figs. 1, 2, and 3; here the end of the specimen is knotted one inchbeyond the slot in member 51 or the slot in clamp 55 to permit movement of one inch under frictional restraint before the specimen breaks. Or, as previously explained, a small stop (not shown) may be clamped to the threadone inch past said slot.

It is necessary to use two different symbols for the energy required to rupture the specimen under the dilfen ent conditions described above. Let C represent the energy for the first or fixed clamp arrangement and let represent the energy for the sliding friction arrangement. The equation F =KC evaluates the energy expended to draw the specimen at a high speed for the selected distance (1 in.) through the friction guide and around the guide pins. This energy must be transmitted from the pendulum, at its moment of maximum speed, through the specimen to overcome the friction and bending at the guide pins. This places the specimen under a tension and produces a strain. (Such conditions prevailto a degree in actual sewing during each stitch formation.)

After energy F :K-C has been expended through the specimen, an'additional quantity of energy, E, must be expended on the specimen to produce rupture. This additional energy is given by the equation E C-F. Substituting K-C for F results in the following formula for the E index in terms of the measured energies C and K,

Another index, L, which may characterize the impact behavior of a thread is The index'L thus represents the percentage of impact energy of the thread which remains and still can be absorbed by the thread after it has absorbed the energy required to ovecome the frictional and bending effects at the guides. The E and L indices are used to evaluate various samples of sewing thread and also for correlation with the results obtained'on the same thread samples in laboratory sewing and in high speed industrial sewing of garments.

As the manner of using the described instrument is made apparent in the foregoing description, no detailed explanation of the operation will be set forth. The device has been found to be quite useful in determinations made at the Philadelphia Quatermaster Depot, U. S. Army of the sewing efiiciency of thread. The described apparatus could also be adapted for testing filaments, yarns, cords, strands, etc.

What we claim is:

1. Apparatus of the character described comprising, in combination, a support; rigid pendulum mounted on the support to swing freely in a vertical plane; a scale plate immovably fixed to the support; an indicator arm swingable over the scale plate to give readings; frictonal mounting means for one end of the indicator arm carried by the support and acting to hold the indicator arm in any angular position until the indicator arm is moved by a superior force; cooperating impact means fixed to the pendulum and to the indicator arm for trans ferring kinetic energy of the pendulum by direct impact to the indicator arm; thread-end-clamping means fixed adjacent the free end of the pendulum; and fixed thread-end-holding means so positioned relative to the pendulum that a thread will be fully tensioned when the pendulum attains substantially vertical position in its free fall, whereupon said tensioned thread will break under the impact of said cooperating impact means.

2. Apparatus of the character described comprising, in combination, a support; a pendulum consisting of a straight rigid rod pivoted at one end upon the support and adapted to swing freely in a vertical plane; a re- Ieasable latch carried by said support above the pendulum and adapted to hold the pendulum in a horizontal position; a scale plate immovably secured to the support; an indicator arm carried by and swingable over the fixed scale plate; means forming a part of the indicator arm mounting to frictionally retard the indicator arm; an impact member attached to the pendulum to swing therewith; a projection fixed to the indicator arm and adapted to be struck by said impact member; the relationship of the impact member and the pendulum being such that the impact member strikes the projection at the instant the pendulum attains its maximum velocity from a free fall; and dual thread-end-holding means secured respectively to the support and to the pendulum and so spaced apart that a thread is put under extreme tension at about the instant of maximum velocity of the pendulum, the pendulum having sutficient kinetic energy to effect breaking of the thread after said instant.

3. The invention defined in claim 2, wherein the specimen'end-holding means that is secured to a support consists of a slotted wedgeshaped member through which a thread may move, the slot of said member being so narrow that when the thread is knotted and then is moved by the pull of the swinging pendulum, the knot will stop movement of the thread causing the specimen to be tensioned and then broken by the energy of the swinging pendulum.

4. The invention defined in claim 3, wherein there is an adjustable means fixed to the support to impose frictional resistance on a thread when it is moved by the pull of the swinging pendulum up to the point of engagement of said knot with said slotted member.

5. Apparatus for testing the strength of thread and the like by means of impact energy and for imposing frictional resistance on the thread under test comprising, in combination, a pendulum of sufiicient rigidity and mass to break a specimen of thread, a support swingably supporting the pendulum, means for securing one end of a thread to the free end of the pendulum, a fixed friction device through which an intermediate portion of the thread may extend, a fixed slotted member through which the thread passes, the other end of the thread being knotted at a predetermined point, the slot of said member being so narrow that the knot in the thread can not pass through it, the thread being of such length that a predetermined length of it will move through the slot responsive to the down pull of the swinging pendulum to bring the knot up against the fixed slotted member thereby tensioning the thread and subjecting it to frictional resistance, further pull of the swinging pendulum stressing the thread to the point of rupture, and a scale fixed to the support to measure in arbitrary units the energy exerted by the pendulum for such rupture.

6. Apparatus for testing the strength of thread and the like by means of impact energy and for imposing frictional resistance on the thread under test comprising, in combination, a pedestal; a pair of uprights fixed to the pedestal; an arm fixed to one of the uprights and extending horizontally; a shaft supported by said uprights and having a horizontal axis; a rigid straight pen dulum fixed to the shaft and swingable in a vertical plane which lies between said uprights; a weight adjustably mounted on said pendulum; a pendulum-holding latch swingably mounted on said arm and depending from its mounting, being adapted to hold the pendulum in a horizontal position; a thread clamp on the free end of the pendulum; a rigid straight impact arm fixed to said shaft and lying in the same plane as said pendulum; a vertical scale plate having indicia marked thereon and fixed to one of said uprights; an indicator arm frictionally mounted on said scale plate at one end of said shaft and adapted to be moved over said scale plate, the friction of the mounting of the indicator arm being such that it will remain in any position to which a superior force moves it; the pendulum when released by said latch swinging downwardly between the uprights with the impact arm spaced outside the uprights but in the plane of a part of the indicator arm so that, with the indicator arm initially properly positioned, the pendulum at the instant of maximum velocity causes the impact arm to strike the indicator arm to cause the latter to move over the scale plate to give a reading; a fixed friction guide through which a specimen of thread travels; a fixed slotted member through which said specimen moves; the specimen having a knot at a predetermined distance beyond the slotted member, and the slot in said member being so narrow that the knot can not pass through it and stops movement of the specimen after traveling said predetermined distance.

References Cited in the file of this patent UNITED STATES PATENTS 1,456,596 Hugentobler May 29, 1923 2,092,439 Bouhuys Sept. 7, 1937 2,359,044 MacBride Sept. 26, 1944 2,518,350 McCormick Aug. 8, 1950 2,625,040 Ireland Jan. 13, 1953 2,651,935 Able Sept. 15, 1953 2,693,108 Eckhardt Nov. 2, 1954 2,706,909 Boor Apr. 26, 1955 

